1. Field of the Invention
The present invention pertains to a method for hydraulically fracturing an earth formation from a wellbore by over-pressuring the wellbore with a pressure drive fluid and using one or more nearby wells in communication with the wellbore to be fractured to act as accummulators for the pressure drive fluid.
2. Background
U.S. patent application Ser. No. 07/874,159, filed Apr. 27, 1992 in the name of Joseph H. Schmidt, et al and assigned to the assignee of the present invention, is incorporated herein by reference. The Schmidt, et al patent application describes improved methods for over-pressuring a well to initiate or extend hydraulic fractures into an earth formation in communication with the well at a sustained flow rate to provide a near wellbore fracture which will not pinch off, in the near wellbore region, in a subsequent conventional hydraulic fracturing operation. The fracturing methods described in the Schmidt, et al patent application include the steps of providing a charge of compressed gas for urging fracturing fluid into the formation upon perforation of the well casing or upon release of the fracturing fluid to flow into the formation from a tubing string closed by a frangible closure member.
The methods described in the Schmidt, et al patent application, as well as the methods described in the prior art of record in the Schmidt, et al patent application, are, however, limited in their effectiveness by the amount of pressure gas charge that may be used to force the fracturing fluid into the formation during the fracture treatment. In this regard, there has been a recognized need to provide additional gas charge at the fracture or breakdown pressure to assure sufficient driving force for the fracturing fluid that is actually forced into the formation and which may include at least some of the gas charge itself. Further in this regard, pressure vessels full of pressure gas may be placed in communication with the well to be fractured. However, there are certain disadvantages to using pressure vessels charged with the pressure driving fluid. Since the fluid pressures required for the fracture treatment are usually relatively high any vessels charged with gas at the required pressures pose additional hazards to operating personnel and structure at or near the wellhead.
Still further, in certain well installations, such as on offshore platforms and the like, there is usually inadequate space for placing the pressure vessels or accummulators which might be used to supplement the pressure fluid charge used to effect the fracturing operation. However, in accordance with the present invention, a unique method has been developed for providing an accumulator for additional fluid charge available for driving the fracturing fluid into the formation to initiate or extend a suitable well fracture, which method is described in further detail hereinbelow.